||The reason is the delivery of new WFC3 UVIS full-frame and subarray bias reference files.
||The ACS WFC bias, dark, CTE dark, and sink files were generated following the ACS WFC anneal on May 28, 2021, and should be used to calibrate ACS WFC observations taken between Apr 27, 2021 and May 28, 2021.
||The previous version of these COS synphot throughput files, 013, had zero throughputs at wavelengths 1189 - 1195.5 Angstroms. The throughputs should be nonzero, and were causing larger than expected discrepancies in ETC release candidate tests. The new files replace the previous files, which are bad.
||These WFC3 UVIS superdarks, drk, and CTE corrected superdarks, dkc, will affect all UVIS data taken from April 22nd - May 16th 2021. Currently, the automated calibration pipeline and Calibration Reference Data System only have WFC3 UVIS drk and dkc reference files up to a USEAFTER date of April 19th 2021. The automated pipeline should now use these reference files to perform dark subtraction on any UVIS datasets obtained between the dates above because they represent the most accurate estimate of the dark current and hot pixels at the time of the science observation. These WFC3 UVIS drk and dkc files were generated using dark exposures from the HST Cycle 28 daily monitoring programs 16395 and 16414. More information regarding the method used to create UVIS dark calibration reference files can be found in WFC3 ISR 2016 08. Additionally, the header of each reference file has a detailed history section outlining the process and provides a list of datasets used to create each file.